Magic angle spinning (MAS) is one of the most useful experimental techniques known to those of skill in the NMR art. By spinning a sample about an axis inclined at an angle of 54.74° with respect to an externally applied magnetic field (B0), high resolution, high sensitivity isotropic spectra can be obtained that are free from line broadenings induced by various spin interactions. MAS has found widespread application in the study of both solid and semi-solid samples, including, e.g., characterization of organic and inorganic solid materials, biological tissue/cell samples, biofluids, and the like. However, gains obtained in spectral resolution and sensitivity often come with corresponding losses in anisotropic information that, in general, provides more structural information than is derived, e.g., from the isotropic shift. Many two-dimensional (2D) spectroscopic techniques are available in the art to obtain or recover missing or lost anisotropic information. In one illustrative approach, anisotropic line shapes, e.g., spinning sideband (SSB) patterns, can be separated using isotropic chemical shift differences in a 2D spectral plane. Projection along the isotropic dimension yields a high resolution spectrum similar to that obtained from MAS.
However, in practice, true in situ investigations remain difficult or impossible to carry out using conventional MAS and constant fast sample spinning because experimental parameters such as pressure, temperature, and feed compositions must be precisely controlled.
Magic Angle Hopping (MAH) and Magic Angle Turning (MAT) are two techniques known in the art that exhibit advantages that if combinable into one operative system and/or device could have potential to meet requirements for in situ investigations.
In MAH, two successive rapid 120° sample rotations are followed by reverse 240° rotations about the magic angle axis. For times prior to the first 120° rotation, between the two 120° sample rotations, and after the second 120° rotation, magnetization is allowed to precess in the transverse (X-Y) plane. Prior to each 120° rotation, a projection pulse is used to project either cosine or sine components of the magnetization to the main field direction. Since only 240 degree sample rotation is involved, tubes can be introduced or coupled to the sample rotor allowing simultaneous control over pressure, feed compositions, and temperature, at a minimum. However, MAH has proven difficult to implement due to difficulties that include maintaining a rotation axis precisely at the magic angle. Any errors with the angle of rotation can result in line broadening along the isotropic dimension. Consequently, spectral resolution with MAH along the isotropic dimension can be much poorer than that obtained from conventional MAS. Thus, MAH has not found wide acceptance for applications.
In Magic Angle Turning (MAT), samples are continuously rotated and read pulses are synchronized to occur at 120 degrees, or ⅓, of a rotor cycle. Compared with MAH, MAT is easy to perform. First, the magic angle in MAT can be set experimentally with high accuracy due to use of a constant sample spinning speed. Second, read pulses can be spaced accurately at ⅓ of a rotor cycle with the aid of an optical detector or other synchronization device. Because slow sample spinning is employed in MAT, large sample volumes can be used to provide high measurement sensitivity. MAT can also be used successfully in conjunction with Phase-Corrected-Magic-Angle-Turning (PHORMAT) sequences to measure chemical shift tensor principle values for complex molecular structures, and to obtain high resolution 1H NMR metabolite spectra and localized spectra of various organs and tissues in small live animals such as mice. However, despite successes obtained with MAT and PHORMAT, to date, rotations at constant speed have not been attained for in situ investigations where pressure control or tubes for controlling feed compositions become necessary.
Accordingly, new systems, processes, and apparatus are needed that provide the ability to conduct in situ investigations, including study of in situ reactions, where pressure control or tubes for controlling feed compositions are necessary.